The WMO says the combined causes of this
historically unprecedented heat are both natural and human - induced: a strong El Niño − the periodic climate phenomenon in the Pacific − and anthropogenic
warming resulting from the rising emissions of greenhouse gases, largely through the burning of fossil fuels, agriculture and deforestation.
Those reanalyses used various tricks, such as the violation of strong statistical conventions relating to the inclusion of principal components, to attenuate the inconvenient implications of the research — specifically, that the
warming from greenhouse gas emissions is
historically unprecedented (Mann, Bradley, & Hughes, 1998) and that those who oppose this scientific fact tend to engage in conspiracist ideation (Lewandowsky, Oberauer, & Gignac, 2013; Lewandowsky, Gignac, & Oberauer, 2013).